Sometimes my blood glucose monitor seems to give incorrect readings. What can I do to make sure the measurement is accurate?

Answers from M. Regina Castro, M.D.

When used correctly, blood glucose monitors — small devices that measure and display your blood sugar level — are usually accurate. But occasionally they may be incorrect.

Consider these factors that affect meter accuracy and the steps to resolve or prevent the problem:

Factors that affect accuracy

Solutions

Test strip problems

Throw out damaged or outdated test strips. Store strips in their sealed container; keep them away from heat, moisture and humidity. Be sure the strips are meant for your specific glucose meter.

Extreme temperatures

Keep your glucose meter and test strips at room temperature.

Alcohol, dirt or other substances on your skin

Wash and dry your hands and the testing site thoroughly before pricking your skin.

Improper coding

Some meters must be coded to each container of test strips. Be sure the code number in the device matches the code number on the test strip container.

Monitor problems

Fully insert the test strip into the monitor. Replace the monitor batteries as needed.

Not enough blood applied to the test strip

Touch a generous drop of blood to the test strip. Don't add more blood to the test strip after the first drop is applied.

Testing site location

If you're using a site other than your fingertip and you think the reading is wrong, test again using blood from a fingertip. Blood samples from alternate sites aren't as accurate as fingertip samples when your blood sugar level is rising or falling quickly.

The amount of red blood cells in your blood

If you are dehydrated or your red blood cell count is low (anemia), your test results may be less accurate.

Blood glucose monitor quality control tests

The following quality control tests can assure you that your meter is working properly:

Test using a control solution. Follow your normal blood-testing procedure, but use a liquid control solution instead of blood. These solutions usually come with your monitor and are available at most drugstores and pharmacies. Follow package directions.

Use liquid control solutions every time you open a new container of test strips, and occasionally as you use them. You generally should also use liquid control solutions if you drop your blood glucose meter, or whenever you get unusual results.

Match your reading with lab results. Take the blood glucose monitor along when you visit your doctor or have an appointment for lab work. Check your blood sugar level with your meter at the same time that blood is drawn for lab tests. Then compare your meter's reading with the lab results. Results that are within 15 percent of the lab reading are considered accurate.

If your meter isn't working properly, contact the manufacturer of your meter and test strips.

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